Sound and picture system



May 7, 1935.` E. H. SMYTHE 4 2,000,198

SOUND AND PICTURE SYSTEM Filed NOV. 14, 1933 2 SheGbS-Sheeb l'llllllllllllilllllll|Illl|l||IlllllIII[IllIlllIlllllllllllllllllllllllllllll|||||l|l|Ill!IllllIllllllllllllllllllllllllllllllllllllllll|||llllllllllllEl D D El D U D D UIIIDUCIDUDE! /////////i///////////////////////l 7 L7U 7 /NVENTOR EHSMVTHE A TTORNEV May 7, 1935. E. H. SMYTHE 2,000,198

' SOUND AND PICTURE SYSTEM Filed Nov. 14, 1953 2 sheets-sheet 2 l F/c;.5.T

33; PHASE a 34 V 35 4 AMPM-m05 1 CORRECTO/1 'm:

/N VEN Tof? By E. HSM? THE Patented May 7, 1935 UNITED STATESPATENroFFIcE `SOUND AND PICTURE SYSTEM Edwin H. Simythe, Evanston, Ill.,assignorto Bell Telephone Laboratories, Incorporated, New York, N.Y.,`a. corporation of NewrYork Application November 14, 1933,seria1'No.-697,9o3

9 claims.v (o1. 179-1003) This invention relates to sound picturesystems, stance, along thef'other side of the central or picand moreparticularly toy amethod and apparatus true-carrying portion .of thestrip in a' position for maintaining a constant and uniform velocitycorresponding to that of the sound track along of movement of the soundrecord film relative to the opposite side of the picture portion; or, ifde- 5 the translating line of light. sired, it may be locatedimmediately alongside '5.

In my copending application, Serial No. 697,901, the sound track. filedNov. 14, 1933, there is disclosed a photo- Although'in the' broaderaspects of the invengraphic sound recording and reproducing system tionthe control or reference" track may be placed in which irregularities ofthe sound record moveupon the film at any time and in any convenient lment due tothe drive side and load side dismanner, as by being imprintedon the film in the 10"'- turbances are compensated for, and relativelyprocess of manufacture, in the preferred'embodiuniform movement of thesound record secured, ment, it is formed' upon the iilm'by the action ofby converting such irregularities of motion as are light simultaneouslyvwith the recording of .the ordinarily communicated to the film intoforces sound track. While the light valve or light coni that operateupon the translating point and controlling device responsive to thesound to be re- 15` tinuously shift its `'position longitudinally withcorded is making'the sound track record, another respect to thedirection of the film movement in light valve or light' controllingdevice actuated by accordance with these irregularities of motion. aconstant frequency oscillator is recording the In the system of mycopending application rereference track. Y'Ilois oscillator is soadjusted as ferred to, the velocity irregularitiesV that are comtoproduce a sinusoidal wave of a frequency rela- 20p pensated'for arethose which are present in the tively high compared with'y theperiodicity of the sprocket that drives the film at or in closeproxhighest'disturbing frequency that 'is to be cornimity to thetranslating point. pensated foriY If the highest disturbing frequency Itis assumed in the copending application reisv assumed to be the 9S-cycleflutter introduced ferredto that the velocity variations of the film bythe sprocket teeth and 'film perforation en- 2 5"` at the translatingpoint are truly represented by gagement, the frequency recorded -uponthe refthe velocity variations of the sprocket that drives erence trackmay be, say, 2,000 cycles per second;

the film or the drum over which the film passes although aconsiderablylower or higher frequency f at the translating'point; and this is acorrect maybeemployed, if desired.

assumption with respect to those disturbances yThe film drivingmechanism of the recorder or 30,

which are introduced into the film movement as a reproducerv isvconstructed and adapted to impart result `of non-uniformity in therotation of the to the'sound record film as uniform a velocity asvarious' elements included in the mechanical may convenientlybe'attained, but need not intrain by means of which the film is driven.But clude the 'ordinarilyiused refinements for supin addition to theseirregularities, the film in its pressing the minor velocity variations.Any pe- 35 movement Ymay still have imposed upon lit riodical departurefrom absolutely uniform veslight velocity variations, such for instanceas are lo'cit'y in `the movement Hof the film in the reintroduced as aresult of the irregularities of encorder produces a correspondingvariation inthe gagement of the sprocket teeth with the film perspacingof thecross-bars or light and dark spaces 40 forations. ofthe recordedreferencefrequency wave onthe 40 jIt is the object of the presentinvention to comreference track, the cross-bars being more closelypensate for'all of the irregularities that are presspaced in theless-than-average velocity part of ent in the film movement; and thisobject is acthe periodical velocity variation of the film, andcomplished byso organizing the system that the being less closely spacedin the more-than-avercompensating shift of the translating line of agevelocity part ofthe periodical variation. K 45 light is controlledimmediately by the velocity In reproducing the sound record from a filmvariations of the film itself rather than intermeupon which a referencetrack has been formed, diately by the velocity variations in the drum orthe reproducing systemr is so organized that `a sprocket which drivesthe film.A In attaining this fixed or' immovable line of light thattraverses the 5o object in accordance with the present inventionreference track acts through the medium of a 50 the sound record filmcarriesl not only the ordiphotoelectric or other light sensitive cell,in asnary sound track but is also provided with an adsociation with anamplifier, resonant circuit and ditional control or reference track.This control rectifier with'properly designed phase and amplior`reference track may be disposed in any contude compensating network, tocontrol the posivenient position upon the film strip, as for intion ofthe line vof'light that passes through the a piece of sound picture filmin which the cross- 'j bars of the reference track are unevenly spacedas a result of velocity variation ofthe nlm at. the time of recording;Figs. 3 and4representschematically arrangements by means ofwhich thesound and reference tracks may be recorded upon the film; Fig. 5represents diagrammatically the mechanical and electrical arrangement ofthe reproducer wherebythe compensating shift of the sound track scanningbeam is'effectedl under vthe control of the'reference track, a lightvalve being used as the agency for effecting the shift; and Fig. 6 is aschematic representation of an arrangement employing a tilting mirror oroscillograph for effecting the compensating shift of the light at thetranslating point.

Referring to the drawings, Figs. 1 and 2 illustrate sections of a soundpicture film II with the picture frames I8 occupying the central portionof the strip, and the sound track I9 extending inthe usual manner alongone side of the central picture strip. The lm strip I1 also carries areference or control track 20 which is illustrated as extending alongthe other side of the picture strip I8, but which may, if desired, beformed in any other convenient location, as for instance, alongside thesound track I9. In the fragment of film strip shown in Fig. 1, thecross-bars of the reference track, recorded upon thelm, as will bedescribed,through the agency of aconstant frequency oscillator and lightvalve or similar device, are represented as being equally spaced. In thefragment of film illustrated in Fig. 2'the crossbars of the referencetrack 20 are represented as being less closely spaced in the region 2|and more closely spaced in the regions 22. Thevspa'cing represented inFig. 1 is such as. results from a uniform velocity of movement of thefilm past the reference track recordingflight, andthe spacingrepresented in Fig. 2 is that which results from a varying velocity ofmovement of the lm strip past the reference track recording light.

Figs. 3 andv 4 indicate schematically themanner in which the referencetrack 20 may be recorded on the lm atthe time when the rsound track I9is recorded. Thesound track recording system is indicatedas consistingof an exciting lamp 23, a condensing lens 24, alight va1ve25 and anobjective lens 26. Similarly the reference track recording apparatusconsists'of the exciting lamp 21, condensing lens 28, lightvalve 29 andobjective lens 3U. The light valves'25 and 29 may be generally of thetype disclosed in the article by Perreault, at page 412 of the August,1932 issue of Bell Telephone Laboratories Record, Vol. X, No. l2. Eachvalve consists of a pair of tightly stretched diamagnetic conductingribbons lying in an intense transverse magnetic field and delining anarrow slit between their proximate edges, the slit extendingtransversely with respect to the length of the photographic film stripIl. f The light slit in the light valve 25 may, in accordance with theusual practice, be of such dimensions as to project upon the sound trackI9 a line of light 1/2 mil or less in height. The light slit in thelight valve 29 may be of such dimensions as to project, if desired, uponthe reference track 20 a line of light somewhat greater in height.

Fig. 4 represents schematically the use of gas discharge lamps forfurnishing the light for recording the sound track and reference trackupon the film. These lamps may be of the negative glow type or thepositive glow type, as desired, the lamp 3l being used for making thesound track record and the lamp 32 for making the reference trackrecord.` As is customary in systems employing glow lamps for recording,the lamps are positionedclose to the film and the limitation of the`recording light to a thin line is elected by means `where desired oneof the tracks may be recorded upon the film by means of a light valveand the other by means of a glow lamp.

The circuits for operating light valves or gas discharge lamps foreffecting the proper modulation of the light for recording sound uponfilm are well known in the art, and it is therefore not thoughtnecessary to illustrate or describe them.

The circuit and apparatus for shifting the position of the sound trackscanning beam in the reproducer under the control of the reference trackon the film is shown in Fig. 5. Light from the filament of the excitinglamp 33 passes through the cylindrical condensing lens 34 and isprojected upon the reference track of the film I1 in the form of a thinbright line of light. Inasmuch as the frequency recorded upon` thereference track may be such a relatively low frequency as 2,000 cyclesper second, the line of light focussed on the reference track may, ifdesired, be several times as thick as-the line of light which scans thesound track, thus permitting a greater quantity of light to pass. Thelight that passes through the reference track is modulated at afrequency which depends upon the spacing of the cross-bars as determinedby the velocity at which the nlm moved in the recorder, and also by therate at which these cross-bars pass the scanning line asdetermined bythe velocity of lm movement in the reproducer. This frequency modulatedlight correspondingly excites the photoelectric or other light sensitivecell 35.

The output of the photoelectric cell after ampliflcation in theamplifier 36 passes through a resonant circuit 31, which is tuned to beresonant at a frequency of, say, 2,200 cycles per second, and which hasa very nearly straight line characteristic between, say, 1,800 and 2,200cycles. In passing this resonant circuit the frequency variationsrepresenting the velocity variations of the recorder and reproducer aretranslated into amplitude variations on account of the increasingattenuation of the resonant circuit, in a substantially straight lineratio, for all frequencies lower than its resonant frequency and in theneighborhood of the average frequency of 2,000 cycles per second of thereference track. The varying frequencies, which now are of varyingamplitudes, are rectified in the detector or demodulator 38. The rectiedcurrents, which correspond in frequency with the rate of variation fromuniform velocity and in amplitude with the amplitude of this variationare preferably subjected to the action of an equalizer in the form of atuned circuit 40 tuned to a frequency representing the differencebetween the resonant frequency of the circuit '31 and the frequency ofthe oscillator that records the reference track. Under the conditionsthat have been assumed, this is the difference between 2,200 and 2,000,or 200 cycles per second.' The equalized output of the rectifier 38 isamplified in the amplifier 39 and passes through the phase and amplitudecorrector 40 to theribbons of the light valve It l .Y The corrector 40may include a bridged condenser of large capacity to correct for phaseshift; and it may also be designed, in accordance with well-understoodpractice, to perform the function whichisperformed by the equalizer 40and permit that element to be'dispensed with.' As a result theribbons-of the light valve are caused to produce a movement of the soundtrack scanning line corresponding in phase and amplitude with thephase'and amplitude of departure of the velocity of the film inrecording and reproducing from its average. velocity. Y l 1 .iV"l'hecorrected current representing the film velocity variations passesin parallel` through the two ribbons of the valve so that both are movedequally in the same direction. Light fromthe exciting lamp 42 isfocussed by the condensing lens 43 upon the slit between the two ribbonsand the image of the slit is focussedby the objective lens system. `uponthe sound trackof the film I1. 'The optical leverage is .such that asthe light valve moves the'slit up the image of theslit is moved down, orVin the direction inY which the film is moving, and vice versa. Afterpassing through thesound track the beam of light .fallsupon thephotoelectric cell 45, and the output of this cell acts through theusualtrain ofampliers and other devices to operate'the loud speaker.

The `.amplitudes Aof variation of film lvelocity from uniform movementin recordingand reproducing, although important from the standpoint ofthe production of perceptible "fiutter or other objectionable effect inthe reproduced sound, are not of themselves of a' great magnitude interms of change of the linear velocityv of film movement. Therefore, forthemost part, they may be compensated for by a movement of the scanningline amounting to only Va Vsmall fraction of an inch, say, 15 or 20mils, along the sound track. Inasmuch as the frequency of the velocityvariations in the film that" are to be compensated for do not exceedbetween and 200 cycles per second, the ribbons of the light valve 4I maybe made longer than those: of the ordinary light valve and' may be tunedto a relativelyglow resonant frequency, thus producingxa greater rangeof movement of the slit with the yexpenditure of lesselectrical-energy.As an example, 'the light valve ribbons Ymay be, say, 2 inches-longinstead of theirusual 1/g-inch length and may be tuned to a resonantfrequency of 1,000 cycles or less as against their usual resonantfrequency of some 10,000 cycles. If the ribbons are 1/2 mil thickandare, say, 26 mils wide, with anoptical ratio of 1:1 between the slit andfilm the line of. light may have a movement along the film Aof about 25mils which is sufiicient .to compensate for all of the ordinaryrecording-and reproducing velocity variations. If a greater lengthofmovement of the scanning line is desired, it may readily be secured byobvious changes in the dimensions cf the light valve ribbons,ror byincreasingthe optical leverage between the light slit andthe'soundtrack.

Fig.A 6 illustrates a modification in `which the compensating shift oftheline of light along the sound track is eifectedvby an oscillatingmirror. Lightzfromthe eXcitingJamp 46 is focussedby the condensing lens41 upon the stationary light slit 48. The light. from the light slitpasses through the objective lens 49 and falls upon theoscillographmirror-VSU, the rotational movement of which isschematically represented as being produced by the energizing -winding5| that is assumed to be traversed by the iiuctuating currents from vthedetector-` 38 (see Fig. 5) after proper compensation with respect tophase and amplitude in a properly designedequalizer and corrector 40.The light that falls upon the oscillating mirror 50 is refie'cted fromthe internal reflecting surface of the prism 52 ontothe sound track ofthe film l1 as the filmpasses over a portion of the periphery of therotating drum or cylinder 53. The'lm may be controlledin its engagementand disengagement with the cylinder 53 by the pressure rollers 513. Thecylinder 53 is so constructed that the portions of it vwhich underliethe sound track and Vreference trackof the film l1 are cut away, inaccordance With'well-understood practice, so that lightpassesunobstructed through the sound track to the photoeleotric cell 55; andalso throughthe reference track vto the associated photoelectric cell,not'shown. As the mirror 50 tilts in response to the velocitycompensating currents, controlled bythe reference track, the image ofthe light slit 48'fo`cussed upon the sound track at a point 56 is movedlengthwise of -th'e soundtrack to compensate for the velocityirregularities introduced in the recording and reproducing operations.

In order to present more clearly the operation of thecompensating systemof fthe invention, it may first be assumed that the movement of the lmpastthe two .translating points or lines of light in the recording'operationhas not been at a perfectly uniform speed, as a result ofvelocity variations havingbeen superposed lupon the uniformrateofmovement. 'I'he result on the recorded reference track isillustrated in Fig. 2. During4 the regions designated by the numerals22in Fig. 2. r f.

f f Let it .be assumed that in thereproduction of the film with suchvelocity irregularities recorded upon the reference track the filmvdriving mechanism operates in such a manner as to draw the film pastthe reference track scanning beam at a perfectly uniform velocity. It isevident'that theV movement of the reference track at a perfectly uniformvelocity past the fixed scanning beam` is accompaniedby the generationof a lower frequency 'in the reference pick-up circuit for thoseportions of the film which have moved at a greater-than-average velocitythrough the recorder, and the reproduction lof a higher frequency in thereference pick-up circuit for those portions olf the filmfthat havemoved through the recorder at a. lower-than-average velocity. Theresultant closer spacing ofV the bars inthe reference track due to alower-than-average velocity of film movement in recording, the soundtrack scanning beam is shifted in the direction of the movement of thefilm, thus producing a relatively less rapid movement between the filmand the sound track translating point; and so that, when the currentthrough the compensating light valve decreases as the result of a lowerfrequency in the reference circuit due to the wider spacing of thecross-bars in the reference track that results from a higherthan-averagevelocity of the film in recording, the sound track scanning beam isshifted oppositely to the direction in which the film is moving so as toincrease therelative velocity of movement between the film and thetranslating point. Therefore, whatever is the instantaneous `rate ofmovement of the film past the line of light of the sound track scanning`beam in recording, this same instantaneous rate of movement'is repeatedbetween the film andthe automatically shifted line of light inreproducing. Consequently allof the recordingirregularities arecompensated for and the reproduced sound is a faithful replica of thesound that made the record.

Again, let it be assumed that the velocity of movement of the lm in therecording operation has been perfectly uniform, but that the velocity offilm movement in the, reproducing apparatus is irregular. The uniformrecording velocity causes the cross-bars of the constant referencefrequency inthe reference track to. be uniformly spaced, as indicated inFig. 1. In the reproducing operation the velocity irregularities ofthe'reproducing apparatus convert the constant frequency yrecorded uponthe reference track into a varying frequency in the reference pick-upcircuit. The greater-than-average velocity half 'of the irregularitycycle superimposed by the reproducing apparatus raises the frequency ofthe wave, .and the less-than-average velocity half of the cycle lowersthe frequency of the wave picked up in the reference circuit. Theacceleration of the` film above its uniform velocity therefore, due tothe operation ofv the resonant circuit, increases the amplitude of thecurrent in the output of the reference circuit and causes acorresponding shift of the sound track scanning beam in the direction ofthe movement of the film, thus producing a relatively less rapidmovement between the film and the translating point. Therefore, therelative rate of movement between the sound track translating line oflight and the film is compensated and remains uniform. The reverseaction takes place during the less-than-average velocityY half of theirregularity cycle, the amplitude of the current in the output of thereference circuit decreasing, and the .compensating light valve shiftingthe soundtrack scanning beam in a direction opposite that in which thefilm is moving, thus increasing the relative velocity of movementbetween the film and the translating point. Consequently, the relativevelocity of movement between the two is maintained uniform.

Inasmuch as the system operates, as has been shown, to compensate eitherfor film velocity'y irregularities introduced in the recording operationor film velocity irregularities introduced inthe reproducing operation,it rfollows. that both vsorts of irregularity are represented in therate of movement of the reference track crossbars past the associatedstationary scanning beam; and that the sound track scanning beam,controlled in position'by this rate of movement, will constantly be so.shifted as to compensate for theL composite' ofl whateverirregularities may have been introduced in recording and reproducing.

Obviously the advantages of the invention with respect to automaticvelocity variation compensation may be realized in the reproduction ofsound recorded on a sound record film, whether the reference yor controltrack has been recorded or placed on the film at the time the sound wasrecorded thereornor whether it is in the form of a uniformly spacedseries of bars or variations placed or imprinted upon the sound film at'some other time to serve as an index of the velocity of movement of thefilm past the translating point. In the latter case the pre-imprintedreference or control track may operate through its associatedinstrumentalities to effect a compensating lshift of the recording lineof light to produce relatively uniform velocity between the film and thetranslating point, as disclosed in my copendingl'application Serial No.697,901, filed Nov. 14, 1933:

' What is claimed is: f

1..A soundv 'translating system arranged to minimize relative motionbetween sound translating elements having two sound translating meansfor translating a sound track for sound reproduction and a referencetrack for registering momentary lm irregularities in velocity of afrequency which causes noticeable sound pitch variation, and means forshifting the sound track translating means commensurate with theirregularities registered by-said reference track.

2. A sound film provided with a sound track for sound reproduction and avelocity reference track, individual translating means for said tracks,and means controlled by said reference track for shifting the soundtrack translating means'responsive to momentary irregular filmvariations.

3. A sound film provided with a constant frequency referencev track andhaving an associated sound translating point, and means controlled bysaid reference track for synchronizing irregular movements of the filmand changes in locationof the point of sound translation.

4. A sound film carrying a velocity reference track and `a sound track,translating means coacting with said sound track at a vtranslatingpoint,'and means controlled by said velocity reference track forchanging the position of said translating point corresponding tomomentary irregular'movements of the film.

5. The method of compensating for velocity variations in the movementpast a translating point of a sound record film provided with areference track, which consists in directly converting velocityvariations of the reference track into corresponding electricalvariations, and utilizing said electrical variations to constantlyadjust the position of the translating point.

6. 'I'he method of producing a sound film provided with a velocitycontrolling reference track, which consists in photographicallyrecordingupon the film' a sound track by means of light varied in accordance withsound, and simultaneously recording upon the film a reference track thecharacteristics of which are constantly varied in accordance with thevariations of velocity of the fihn as the sound track is recordedthereon.

7. In a sound film recording and reproducing system, means forsimultaneously recording upon a photographic film a sound track and aconstant frequency reference track, and means controlled by saidreference track in reproduction for causing the sound track translatingpoint to be shifted an amount commensurate with the irregularities inthe movement of the sound track past its translating point in recording.

8. In a sound film reproducing system, a sound record film bearingthereon a sound track and a reference track representing a constantIrequency record, translating means having a translating point coactingwith said sound track arranged to shift said translating point, andmeans under the control of said reference track for controlling saidtranslating means for changing the position of the translating pointproportional to momentary variations innlm velocity of a nature to causesound distortion.

9. In a sound film reproducing system, a sound record nlm having a soundtrack and a reference track, translating means for said sound trackhaving a translating point, at which the record upon said sound track istranslated into electrical currents varying in; accordance with therecorded sound, translating means for said reference track having astationary translating point at which the variations recorded upon thereference track are converted into corresponding

